I would say that you have an obstruction in the mixing tube, and it is diverting gas outside of it. The POP that you see is a mass of propane igniting outside the burner. Shut the gas off until you have it fixed, it is a hazardous situation.
Larry & Cheryl Oscar, Louie, Ranger & Henry (our Springers)
2010 Allegro RED 38QBA "Harvey"
2009 Honda Element "Towster"